16 TECHNICAL CONSIDERATIONS Understanding the nature of noise The noise given off by a particular source can usually be categorised into one of the following forms: Structure-borne noise - is the sound generated by a vibrating source or impact event. The acoustic energy created by these vibrations is transmitted into the structure of a building (e.g. floors, walls, pipework etc) or into mechanical elements (e.g. metal frames, panel work, supports etc). This energy travels through solid structures and is released as air-borne noise at different locations within the building or mechanical system. Air-borne noise - is the sound that travels through the air and into the surrounding environment. In closed environments such as rooms and enclosures, air- borne sound may reverberate and increase the levels of noise both in and outside the contained space. Most forms of noise will contain contributions from both air-borne and structure-borne sound. Although measures can be taken to limit structure- borne components, such as by isolation and damping; air-borne sound can only be treated with the use of absorbing materials. Open cell foams such as ArmaSound and ArmaComfort have an extremely high absorption performance per unit thickness, offering a solution for the most demanding applications. In many cases, acoustic materials provide a low cost method of controlling noise, and if correctly applied, will significantly reduce the overall noise levels. Many types of materials may be used to control both structure-borne and air-borne noise and are split into the following four categories: • Sound absorption - Absorbers • Sound transmission loss - Barriers • Vibration isolation - Decouplers • Vibration damping - Dampers Primarily, absorption and transmission loss (barrier) materials control air-borne noise while damping and isolation materials control structure-borne noise. Armacell’s acoustic insulation solutions, for use in apartment, office and hotel buildings as well as electronic equipment and enclosures, help meet the demanding requirements for noise reduction. Waste water and drainage pipework Occupants of hotels and buyers of luxury apartments in particular expect a high level of sound control, with nuisance noise from running water services a real source of distraction. Due to the way in which waste water pipes are routed within the building, the water flow reverberates within the pipe and the amplified noise breaks out – partly through the pipe wall itself but primarily through coupling points. Coupling points act as acoustic bridges through which noise can travel in the form of vibrations, exciting other surfaces to vibrate and creating a “loudspeaker” effect. As a result waste water pipework can radiate nuisance noise throughout a building. Decoupling pipework Introducing a visco-elastic resilient layer between the pipe and the structural connection points has the effect of decoupling the acoustic bridge – significantly reducing the breakout noise. ArmaComfortABAlu,TubolitARFonoblokandTubolitAR Fonowave are thin and highly cost effective decoupling materials that are proven to reduce noise breakout from waste water pipework. Aside from decoupling, these materials also perform a role damping vibration in the pipe wall – reducing the overall noise breakout. Ductwork acoustics If left untreated, both structure-borne and air-borne noise travels along duct networks with little attenuation - even over large distances. There are typically four ways in which the noise from ductwork may transfer into the living or working space: • Air-borne propagation noise • Break-out & break-in noise • Duct wall vibration • Acoustic bridging Internal lining Internally lining ductwork using a sound absorbing material is the most effective way of reducing both air- borne and breakout noise. In addition, any sufficiently visco-elastic material applied inside the duct wall will also restrict vibration. The Armacell range of elastomeric insulation materials are particularly well suited to internally lining ductwork. Being dust and fibre free there is no risk of fibre migration and no need to cover ArmaFlex or ArmaSound RD materials. ArmaFlex is also uniquely resistant to bacteria and mould growth owing to the in- built Microban® antimicrobial protection. ACOUSTICS